The overall objectives of this proposal are to contribute to an understanding of the biochemical mechanisms that ultimately result in the biosynthesis of carbohydrate-containing macromolecules, such as polysaccharides and glycoproteins. Such understanding will be sought by studying reactions involving the synthesis and inter-conversion of sugar nucleotides, key precursors in polysaccharide and glycoprotein synthesis. Specifically, four related enzymes are being or will be studied: 1. UDP-galactose 4-epimerase (UDP-galactose yields (reversibly) UDP-glucose). 2. UDP-L-arabinose 4-epimerase, (UDP-L-arabinose yields (reversibly) UDP-xylose). 3. UDP-galacturonate 4-epimerase, (UDP-galacturonate yields (reversibly) UDP-glucoronate). 4. UDP-glucuronate carboxy-lyase, (UDP-glucuronate yields UDP-xylose plus CO2). A major goal of this research project is to understand enzymatic reactions in which DPN is not a stoichiometric reaction partner, but functions as a redox catalyst at the active site of the enzyme. A major effort will be directed towards the purification of such enzymes, where such purification has not been achieved as yet, a thorough study of their kinetic and physical properties, and preparation of sufficient quantities of purified enzymes to allow detailed investigation of the relationships of their reaction mechanisms. Intermediates found in the UDPGalUA epimerase and UDPAra epimerase reactions will be tested in the UDPGlUA carboxy-lyase reaction to demonstrate their involvement in the enzymatic decarboxylation of UDPGlcUA.